1. Field of the Invention
The present invention relates to a device for measuring various quantities concerning a flow, among others, relates to a flow rate and flow velocity measurement device using a detection element integrally formed on a detection element and/or a semiconductor chip depending on temperature, and relates to a measurement device suitably applied, for example, as a combustion controlling mass flow rate sensor of an engine for a vehicle or industry, or a mass flow rate sensor for an industrial air conditioning system and compressor pressurized air supply system and, furthermore, an air/fuel ratio controlling flow rate sensor of a domestic gas hotplate.
2. Description of the Related Art
In an engine combustion controlling mass flow rate sensor for a vehicle, an output change due to a pollution substance accumulation onto a detection element is a great problem. In order to solve this problem, in Japanese Patent Laid-Open No. 193863/1996 Gazette and the like there is proposed xe2x80x9cto prevent an accumulation of pollution substance onto and an action of reverse flow on the detection element by providing a housing structure with an auxiliary passage for deflecting a part of air from a main air flow and a suitable opening portionxe2x80x9d.
However, the housing structure of a sensor disclosed in the Japanese Patent Laid-Open No. 193863/1996 Gazette is effective for accumulation prevention of a pollution substance whose density is much higher than that of a measurement fluid but, as to the pollution substance whose density is relatively low, there is a fear that it enters into a divided flow passage and is accumulated onto the detection element. Further, in this sensor, since it is excessively intended to exclude an influence of the reverse flow, it becomes difficult to measure the reverse flow.
By the way, recently, in order to cope with an emission regulation and the like, there is desired a further high performance combustion controlling mass flow rate sensor, for example, a sensor capable of detecting both of normal flow and reverse flow. Incidentally, hitherto, also a flow passage structure of the sensor capable of detecting the reverse flow has been proposed but, in the case where the reverse flow is measured, a detection output of the same level as the normal flow has not been obtained, so that it is considered that a detection output correction by a control circuit is necessary.
An object of the invention is to provide a measurement device concerning a flow, in which an accumulation of the pollution substance onto the detection element is prevented. A further object of the invention is to provide a measurement device concerning a flow, which is capable of measuring the reverse flow similarly to the normal flow.
A measurement device of a first aspect of the invention has: a divided flow pipe which has a divided flow pipe passage basically curved in xcexa9-shape form, and into which a flow in a main flow pipe, that is a detection object, is introduced; an inlet port of the divided flow pipe, which is formed in an outer peripheral side of the divided flow pipe, and opens in a face approximately orthogonal to a flow direction in the main flow pipe; a partition formed in the divided flow pipe; plural branch flow passages divided/formed by the partition so as to mutually branch and join in the divided flow pipe; and a detection element which is disposed so as to be exposed to a flow in, among the plural branch flow passages, the branch flow passage formed in the outer peripheral side of the divided flow pipe, and detects a quantity concerning the flow.
In this measurement device, in the divided flow pipe, a measurement fluid introduced into the divided flow pipe is sharply changed in its direction before it arrives an inlet of the branch flow passage in which the detection element exists. Therefore, the pollution substance whose inertia is high is prevented from entering into the branch flow passage in which the detection element exists. In addition, in the divided flow pipe, by means of further dividing the flow by the partition, it is possible to reduce a Reynolds number of the flow toward the detection element (because a flow sectional area becomes small), so that the flow in the vicinity of the detection element is adjusted and it is possible to perform a high accuracy detection. That is, according to this measurement device, by effectively branching the measurement fluid and changing it in its direction, in regard to both of the pollution substance mixed in the measurement fluid whose density is higher than that of the measurement fluid and the pollution substance whose density is relatively low, these pollution substances are all prevented from accumulating on a detection face of the detection element, so that there is provided a measurement device which is excellent in pollution resistance and whose detection output change is low over a long period.
In a measurement device of a second aspect of the invention, the divided flow pipe has a flow passage structure basically symmetrical with the detection element being made a center. According to the flow passage structure of such a symmetrical structure, since the flow in a divided flow pipe passage for the normal flow and the flow in the divided flow pipe passage for the reverse flow become symmetrical, it becomes unnecessary to particularly compensate a detection output in case of the reverse flow.
Preferably, by constituting the measurement device on the basis of the first and second aspects, as well as being excellent in pollution resistance, a similar detection output level can be obtained in regard to both of the normal flow and the reverse flow.
A measurement device of a third aspect of the invention has: a detection element which is disposed so as to be exposed to a flow in, among the plural branch flow passages, the branch flow passage formed in an inner peripheral side or an intermediate portion of the divided flow pipe, and detects a quantity concerning the flow; and a throttle formed in a flow passage between an inlet port of the divided flow pipe and an inlet of the branch flow passage in which a detection face of the detection element is exposed to the flow therein. In this manner, in case where the detection element is exposed to the branch flow passage of the inner peripheral side or the intermediate portion in which a direction change of the flow introduced into the divided flow pipe inlet port is relatively small in comparison with the branch flow passage of the outer peripheral side, the accumulation of the pollution substance onto the detection element is suitably prevented by providing the throttle.
A measurement device of a fourth aspect of the invention has: a divided flow pipe which has a divided flow pipe passage basically curved in xcexa9-shape form, and into which a flow in a main flow pipe, that is a detection object, is introduced; an inlet port of the divided flow pipe, which is formed in an one end outer peripheral side of the divided flow pipe passage, and opens in a face approximately orthogonal to a flow direction in the main flow pipe; an outlet port of the divided flow pipe, which is formed in the other end top of the divided flow pipe passage, and opens in a face approximately parallel to a flow direction in the main flow pipe; a partition which is formed in the divided flow pipe, one end of which extends till a vicinity of the inlet port, and the other end of which extends while being spaced from the outlet port; plural branch flow passages divided/formed by the partition so as to mutually branch and join in the divided flow pipe; and a detection element which is disposed so as to be exposed to a flow in, among the plural branch flow passages, the branch flow passage formed in an outer peripheral side of the divided flow pipe, and detects a quantity concerning the flow. Since this measurement device has an asymmetrical flow passage structure, it is suitable especially in case of measuring the normal flow.
A measurement device of a fifth aspect of the invention has an inlet port of the divided flow pipe and an inlet of the branch flow passage, which are mutually formed such that the flow introduced into the divided flow pipe is changed in its direction and flows into the branch flow passage in which the detection element is exposed to the flow therein.
A measurement device of a sixth aspect of the invention has a throttle formed in a flow passage between the inlet port of the divided flow pipe and an inlet of the branch flow passage such that the flow introduced into the divided flow pipe is changed in its direction and flows into the branch flow passage in which the detection element is exposed to the flow therein.
A measurement device of a seventh aspect of the invention has a Venturi provided, on a wall face of the partition opposite to the detection element and from an upstream to a downstream of the detection element, such that a flow passage of the branch flow passage in which the detection element is disposed is made narrowest in the vicinity of a center of the detection element.
Other aspects and characteristics of the invention are as set forth in each claim and, with its citation, a repetitionary description is omitted. Therefore, it is deemed that each characteristic of each claim is set forth here. Incidentally, a dependent claim can be applied respectively to each independent claim so long as it is not contrary to a principle of the invention set forth in each independent claim and, further, the dependent claim can be applied to another dependent claim.
Hereunder, preferred implementation modes of the invention are explained.
In the preferred implementation mode of the invention, an end portion of the partition does not extend to just below the inlet port of the divided flow pipe, and an inlet of the outer peripheral side branch flow passage in which the detection element is exposed to the flow therein does not open just below the inlet port of the divided flow pipe. By this, the pollution substance is prevented from advancing straight from the divided flow pipe inlet port toward the branch flow passage inlet.
In the preferred implementation mode of the invention, there is formed a bypass flow passage short-circuiting between the inlet port and the outlet port of the divided flow pipe without passing through the plural branch flow passages. By this, the flow introduced into the divided flow pipe is stabilized and, further, the measurement fluid (flow in the main flow pipe) becomes easy to be taken into the divided flow pipe. Especially, in case where the flow passage structure of the divided flow pipe is formed symmetrically with the detection element being made a center, by providing an orifice reducing the bypass flow passage or a flow sectional diameter of the bypass flow passage, it is possible to intend to stabilize the flow reaching the detection element in regard to both of the normal flow and the reverse flow.
In the preferred implementation mode of the invention, the orifice is provided in the bypass flow passage, and a flow rate of the measurement fluid toward the detection element is set by a protrusion amount of a flow passage wall forming the orifice or an orifice open area. By this, it is possible to quantitatively control the flow rate toward the detection element.
In the preferred implementation mode of the invention, in the divided flow pipe, there is provided means for forming such a flow as obliquely impinging against a detection face of the detection element. By this flow control means, a flow to be detected is constantly supplied to the detection face of the detection element, so that it is considered that it follows that the flow to be detected surely flows on the detection face. In addition, since generations of vortex flow and exfoliation in the vicinity of the detection face are suppressed, it is considered that a detection accuracy and a reproducibility are improved.
In the preferred implementation mode of the invention, as the flow control means for forming a flow (down flow) obliquely impinging against the detection face of the detection element or a flow flowing obliquely with respect to the detection face, there is provided a flow passage face protruding than the detection face in at least an upstream, or an upstream and/or a downstream of the detection element. As a form of the protrusion, one capable of forming the flow obliquely impinging against the detection face suffices and, preferably, it is protruded concavely or convexly or its protruding surface is made a linear, polygonal or concave curved form slant face.
In the preferred implementation mode of the invention, in a curved portion of the divided flow pipe (detection pipe), the detection face of the detection element is exposed inside the divided flow pipe. Further preferably, a curved pipe (divided flow pipe) is attached in a direction orthogonal to the main flow pipe (measurement object pipe), and the detection element is provided in this curved portion (folded portion, a portion where the flow passage is curved) of the curved pipe. Alternatively, the detection element is disposed in a portion where the flow in the divided flow pipe is inverted or a portion where the flow direction is sharply changed or its vicinity. Also preferably, the detection face of the detection element is exposed to a portion where the flow in the divided flow pipe is speedy. Also preferably, the detection face of the detection element is exposed to a portion where the flow is throttled and subsequently changed in its direction in the divided flow pipe or its vicinity.
In the preferred implementation mode of the invention, such a detection element as mentioned below is used. That is, this detection element is one in which basically four thin film resistors are provided in a semiconductor chip. More concretely, a diaphragm portion and a rim portion are provided on a semiconductor layer. In the diaphragm portion, there are provided (1) an upstream temperature sensor, (2) a downstream temperature sensor, and (3) a heater disposed between the upstream temperature sensor. On the other hand, in the rim portion, (4) an atmosphere temperature sensor is provided. The diaphragm portion is made very thin and a heat insulation is intended.
Next, a principle of detecting various quantities concerning a flow such as flow velocity and flow rate by using this detection element is shown as follows.
(1) An electric power supplied to the heater is controlled such that the heater has a constant temperature difference with respect to an atmosphere temperature.
(2) Accordingly, in the case where there is no flow, temperatures of the upstream temperature sensor and the down stream temperature sensor are approximately the same.
(3) However, in the case where there is flow, the temperature of the upstream temperature sensor descends because a heat escapes from its surface. As to the temperature of the downstream temperature sensor, since a heat input from the heater increases, a temperature change is smaller than that of the upstream temperature sensor. Incidentally, there is also a case where the temperatures of the downstream temperature sensor ascends.
(4) On the basis of a temperature difference between the upstream temperature sensor and the downstream temperature sensor, the flow rate and the flow velocity etc. are detected and, from a sign of the temperature difference, a flow direction is detected. Incidentally, the temperature difference can be detected on the basis of a change in electrical resistance by the temperature.
In the preferred implementation mode of the invention, it is one for, on the basis of temperature, measuring the quantity concerning a flow, at least including a flow rate and/or a flow velocity by the detection element.
In the preferred implementation mode of the invention, the measurement device according to the invention is installed in an intake system of engine of various vehicles, and can be applied to a measurement of intake quantity etc. of the engine mounted on a two-wheel or four-wheel vehicle. For example, the measurement device according to the invention is installed between an air cleaner and a throttle valve in the intake system of engine mounted on the four-wheel vehicle. Further, the measurement device according to the invention is attached, in the intake system of engine mounted on the two-wheel vehicle, to a two-wheel vehicle intake pipe (air funnel) connected to a cylinder in order to measure a flow rate or a flow velocity etc. of the intake.